My CTDi I can hear a slight turbo release when changing but its very subtle and always been there, but its the release of air and no rattles. Does it only do it between 2nd and 3rd or can you get it to recreate the sound regardless of what gear you are in, or whether you are moving or not?

noises are very subjective and sound different to one person and the next. is it a rattle? is it wastegate flutter? without experiencing or hearing the noise its difficult to comment to be honest. I caunt say there is anything that I have experienced similar to a rattle as described by @Wizard

I had the front wheels off this morning to clean and copper ease the brake pads mounts as I've been getting a honking noise every now and again while moving very slowly. Whilst car up on the stands I had a look through at the wheel arch to have a prod and poke to find loose things.

All exhaust rubbers are good.

I did notice that a rod with a threaded end on the turbo was loose and when gently prodded with my jack handle rattled and could be my noise.

Would that rod be in same position as when engine not running when you rev the engine to 3000 RPM and remove foot from the throttle?

I've mentioned that you also get the noise when changing up through the gears, most noticeable from 2nd to 3rd due to less road noise I guess. If when I change up I hold the throttle for a split second I don't get the noise!